Electrophotographic device

ABSTRACT

An electrophotographic device which comprises a detector which detects the entry of a sheet-shaped material provided in the path of the sheet-shaped insulating material to a development station including a developing electrode divided into smaller portions in the direction perpendicular to the direction in which the sheet is advanced, closing and opening circuits for application of electric potential to the portions of the developing electrode, and a delay circuit which receives the signal from the detector and makes the circuits close so as to apply electric potential only to the portions of the electrode confronting the sheetshaped insulating material.

United States Patent 1191 Matsumoto et al. 14 1 Jan. 2, 1973 54 ELECTROPHOTOGRAPHIC DEVICE 3,328,193 6 1967 Oliphant et al ..117 37 3,441,345 4/1969 Kolibas ..355/10 [75] ig r Tama" both 3,345,925 10/1967 Ostensen ..118/637 3,474,019 10/1969 Kriegeret al ..117/37 [73] Assignee: Fuji Photo Film Co., Ltd., Ashigar 3,577,259 5/1971 Sato et al ..118/637 Kamigun, Kanagavva, Japan Primary Examiner-Mervin Stem [22] Filed: 1971 Assistant Examiner-Leo Millstein [2]] Appl 1 97 Attorney-Gerald J. Ferguson, Jr.

[57] ABSTRACT [30] Foreign Application Priority Data 6 I I An electrophotographw device wh1ch comprises a de- Jan. 9, Japan the entry of a sheet shaped material provided in the path of the sheet-shaped insu- [52] US. Cl ..118/7, 117/37 LE, ll8/DIG. 23, lating material to a development station including a 118/637 355/10 developing electrode divided into smaller portions in [51] Il lt. Cl ..B05c 11/00 the direction perpendicular to the direction in which [58] Field of Search ..118/7, DIG. 23, 637; the sheet is advanced, closing and opening circuits for 117/37 LX; 355/10 14 application of electric potential to the portions of the 0 developing electrode, and a delay circuit which [56] Rekrences C'ted receives the signal from the detector and makes the UNITED STATES PATENTS circuits close so as to apply electric potential only to the port1ons of the electrode confronting the sheet- 3,137,306 6/1964 Cunha et al. ..134/46 shaped insulating material. 3,547,076 l2/l970 Saklikar ....l18/637 3,415,223 12/1968 Zweig ..118/637 10 Claims, 5 Drawing Figures PATENTED JAN 2 [975 ENT0R$ SEIJI MATSUMOTO YASUO TAMAI BY FERGUSON {fBHKE/ ATTORNEYS.

ELECTROPHOTOGRAPHIC DEVICE BRIEF EXPLANATION OF THE DRAWING FIG. 1 is a schematic side sectional view of the ordinary reversal liquid developing device for electrophotography,

FIG. 2, FIG. 4 and FIG. 5 are schematic diagrams of the important parts of the device for working the present invention and FIG. 3 is a schematic diagram illustrating one embodiment of the control device designed to permit the electric field to act only on a sheet-shaped insulating material.

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an electrophotographic device for causing more developing particles to be deposited effectively on portions of an insulating material having less electric charge.

As is known universally, when an electrostatic latent image contained in an insulating material (such as layer of photoconductive insulating substance, for example) is brought closer to developing particles (hereinafter referred to as toner) having electric charge of a polarity similar to that of the electric charge with which the latent image is formed, the particles are repelled by the electrostatic repulsive force in portions rich in electric charge and therefore are deposited on portions devoid of electric charge. In the case of a toner image formed by such reversal development as this, the toner is not deposited by virtue of electrostatic attraction. It is deposited in accordance with the strength of surface electric field and not in proportion to the density of electric charge with .which the electrostatic latent image is formediConsequently, the toner is deposited in a larger quantity near portions where there occurs a large difference in density of electric charge and very little toner is deposited at portions where electric charge is uniformly small. As a means for eliminating this shortcoming, there has been known a method whereby DC voltage equaling the surface electric potential at portions of electrostatic latent image having the maximum electric charge density is applied to the development electrode so that an electric field proportional to the difference from the maximum electric charge density may be produced between the developing electrode and the insulating material at portions of less electric charge to effect satisfactory development (hereinafter referred to as reversal Developing method).

In the device for working this reversal developing method, when the insulating material to be developed is placed close to the developing electrode, the toner is deposited on the surface of insulating material in accordance with the electrostatic latent image formed thereon. In case where the insulating material containing the electrostatic latent image is not a long continuous roll but is a comparatively small sheet in shape and such sheet-shaped insulating material is fed intermittently to the developing device to be developed, there can be occasions on which there is no sheet close to the developing electrode. On such occasions, the electric potential being applied to the developing electrode causes the toner to adhere wastefully to the interior of the developing device and toner is extremely wasted. As a consequence, the toner is wasted heavily and the interior of device is smeared.

FIG. 1 illustrates one example of the device for working such ordinary reversal developing method. The container 1 is filled with what has toner dispersed in an insulating liquid (hereinafter referred to an liquid developing agent) 10, with a developing electrode 4 and an endless carrier belt 5 disposed in the state immersed in saidliquid developing agent. The developing electrode 4 and the carrier belt 5 are both electroconductive and the electric potential is applied by means of the power source 8 so as to produce an electric field between them. The carrier belt 5 is revolved in the direction indicated by the arrow mark 6 by means of rollers 7 and 7' so as to fulfil the function of carrying the sheet 2 containing therein an electrostatic latent image 3 into the gap 11 between the developing electrode 4 and the carrier belt 5 and then carrying out the sheet along the guide 9. While the sheet 2 passes the gap 11, the electrostatic latent image 3 formed thereon is developed by the toner having the electric charge of the same polarity as that of electrostatic image. However, since the electric field existing at the gap 11 generally tends to be cancelled by the electric potential of the electrostatic image, nothing is available for cancelling the electric field of the gap 11 while the sheet 2 is not in existence at the gap 11. Consequently, the electric field of the maximum magnitude causes the toner to adhere to the carrier belt, with the result that the toner existing in the liquid developing agent will be wasted heavily. Besides, the carrier belt itself becomes smeared to an increased extent. One may conceive an idea of applying the electric potential between the developing electrode 4and the carrier belt 5 only in the period the sheet is in the gap 11 and suspending the application thereof while the sheet 2 is not existing in the gap 1 1. In this case, the application of electric potential must be continued until the sheet 2 has departed completely from the opening 11 and, therefore, the electric field develops at the portion of opening 11 in which the sheet 2 is partially absent so far as any portion of the sheet 3 is still in existence in the gap 11. Thus, the toner is continuously deposited on the carrier belt.

The present invention relates to an electrophotographic device which has a solution to such problem.

Now, the present invention is described with reference to the drawing.

FIG. 2 illustrates one example of the reversal developing device for electrophotography according to the present invention. The sheet 2 to be developed is forwarded by rollers 30 and 30' along the guide 9 into the gap 11. The means 12 and 12' which serve to detect the entry of the sheet 2 sense the forward end position of the sheet. The detecting means 12 and 12 are, for example, of such principle that infrared ray is transmitted from the means 12 and received (or sensed) by the means 12' and the entry of the sheet can be detected by the fact that the sheet 2 intercepts the infrared ray and consequently prevents it from reaching the infrared ray detecting device 12'.

The signal issued upon detection of the forward end of sheet causes electric potential to be applied to the developing electrode, with due time allowance given to the delay which occurs before the sheet 2 arrives at the gap 11. The developing electrode 14 is divided into smaller portions in the direction perpendicular to the direction in which the sheet is advanced. As the sheet 2 enters the gap 11, one of the switches 15 is closed on the division of electrode existing at the leftmost position in the diagram to initiate application of electric potential thereby. As the carrier belt 5 advances the sheet further along the gap 11, the remaining switches of the divided developing electrode are closed one after another in the direction toward right synchronously with the conveying speed of the endless belt 5 to provide gradually extending application of electric potential. In this manner, the electrostatic latent image formed on the sheet 2 is developed. In the device shown in FIG. 2, both liquid developing agent and container are identical with those shown in FIG. 1 and are omitted from the diagram. As the sheet 2 moves on toward right, the tall end thereof is detected by the detecting means 12 and 12' and, when the tail end of the sheet has completely passed the leftmost division of developing electrode with a given delay, the switches 15 are opened in sequence to stop the application of electric potential to the developing electrode gradually. As the sheet 2 is forwarded by the carrier belt 5, the tail end moves on toward right and the switches 15 are gradually opened synchronously with the conveying speed. Consequently, the electric potential is removed at portions of gap 11 from which the sheet has been removed, whereby the wasteful consumption of toner within the liquid developing agent can be prevented.

In this device, there may be incorporated a circuit which permits the application of electric potential to be retained for a fixed length of time as from the time of detection of the passage of the forward end of sheet where the conveying speed of sheet is kept constant.

If the duration of the application of electric potential to the electrode is slightly shorter than the time required for the sheet to pass under the electrode completely, the developing speed is, as a matter of course, decreased though to a small extent. Although this is not desirable, it is still much better than when the duration is excessively long.

FIG. 3 illustrates one example of the delay device for controlling the switch which functions to start and stop the application of electric potential to the developing electrode. It functions to cause the output from the sheet detecting device 12 to be amplified by means of the amplifier l6 and to close the switch 18 by means of the relay when the sheet remains at the position of detection. Numeral l7 denotes a means for exciting the magnetic recording ring head 19 with an AC power source of about 1,000 c/s. The magnetic recording head 19 is excited by the closure of the switch 18. Consequently, the magnetic recording tape 22 is magnetized and the signal is recorded thereon. The tape moves as indicated by the arrow mark 23. This movement corresponds to the motion of the sheet. For example, it moves at a speed which is equal to or one of several divisions of the driving speed of the endless belt. Therefore, the portion at which the signal has been recorded moves toward right in the diagram and reaches the portion directly below the group of signal reading heads 25. The fact that the portion of the tape at which the signal has been recorded reaches the reading head at the leftmost position corresponds to the fact that the sheet just reaches the left end of the gap 11 in the diagram of FIG. 2. With the movement of the tape,

the portion of recorded signal moves to the right and, at

the same time, reaches the reading head of the next group of heads 25. This is almost synchronous with the motion by which the sheet is made to reach the corresponding portion of the division of developing electrode. The signal which has been read out by the reading head is then amplified by the amplifier 24 and the resultant output functions to close the switches 15 of FIG. 2 so as to permit electric potential to be applied to the corresponding divisions of developing electrode by means of relays.

As the tail end of the sheet has completely passed the detecting device 12, the switch 18 is opened and the recording head 10 is deprived of excitation. The signal recorded on the magnetic tape 22 is no longer in existence, because the magnetic tape has already been treated with a permanent magnet 20 to erase the signal. With a delay of a fixed length of time, the portion of the tape from which the signal has been erased reaches the group of reading heads 25 and reading of signal no longer occurs. Consequently, the switches 15 in the diagram of FIG. 2 are opened so as to stop the application of electric potential to the developing electrode one after another from the left. Thus, electric potential is applied only at portions of the gap 11 illustrated in FIG. 2 where the sheet 2 exists. Since no electric field exists at portions where the sheet is no longer in existence, waste of toner can be prevented.

FIG. 4 illustrates an example wherein a multiplicity of electroconductive rollers 26 of a small diameter employed to function as developing electrodes are moved by a motor not shown in the diagram so as to smoothen the passage of sheet along the gap.

FIG. 5 is an example of the device adapted to permit the electric potential being applied to the divided developing electrode to be varied so as to prevent possible adverse effect due to such phenomenon as dark decay of electrostatic image on the sheet. It is generally desirable to keep the potential at a higher magnitude on the side the sheet enters the device and at a lower magnitude on the side the sheet departs from the device. Numeral 27 denotes a group of resistors which serves to divide the electric potential of the power source 28. By means of this group of resisters 27, the electric potential being applied to the divided developing electrode can be varied.

The description made to this point has covered a reversal developing device. The device of the present invention can also be utilized for permitting the toner to be deposited substantially uniformly throughout the entire surface of a sheet containing no electrostatic latent image. In other words, it can be used as a means for supplying the toner without any wasteful consumption of toner or smearing the device interior. This means that it can be used for the preparation of toner sheet.

What is claimed is:

1. An electrophotographic device, characterized by gradually closing and gradually opening circuits for application of electric potential to the developing electrode so as to synchronize the application of electric potential with the relative movement of a sheet-shaped insulating material with respect to the developing electrode, whereby electric field will be generated only at the portion of the aforementioned developing elec- 3, wherein later portions of the divided developing electrode are applied to decreased potential.

5. An electrophotographic device which comprises a detector which detects the entry of a sheet-shaped material provided in the path of the sheet-shaped insulating material to a development station including a developing electrode divided into smaller portions in the direction perpendicular to the direction in which the sheet is advanced, closing and opening circuits for application of electric potential to the portions of the developing electrode, and a delay circuit which receives the signal from said detector and makes s'aid circuits close so as to apply electric potential only to the portions of the electrode confronting the sheetshaped insulating material.

6. An electrophotographic device as claimed in claim 5, wherein said delay circuit comprises a magnetic recording tape carried synchronously with the transportation of the sheet, a magnetic recording head confrontingsa'id recording tape and excited by the signal from the detector, and plurality of heads which read the-signal on the tape and put out the signal to close detecting means for sensing the presence of said sheet along its path of movement; at least one source of potential; and

actuating means responsive to said detecting means,

for sequentially energizing said development electrode means as said sheet is moved adjacent the successively energized development electrode portions and for sequentially de-e'nergizing said development electrode portions as said sheet is moved away from the successively de-energized development electrode portions whereby said source of potential is only applied to those development electrode portions which are adjacent the sheet as it moves adjacent the development electrode so that the toner is substantially deposited only on the sheet and not the carrier therefor. 8. The improvement as in claim 7 where said detecting means is disposed a predetermined distance from aid d velo ment ele tode, said im rovement' luding ,delay rrleans for delaying the on put from 5233 detecting means until the forward end of said sheet reaches the first of said plurality of development electrode portions.

9. The improvement as in claim 8 where said delay means includes a movable storage medium, the output from said detecting means being recorded thereon, and where said actuating means includes (1) a plurality of switching means connected between said potential source and said plurality of development electrode portions respectively and (2) a plurality of sensing means successively disposed along a portion of said movable storage medium and respectively connected to said plurality of switching means, the first of said sensing means being disposed a predetermined distance from where the output from said detecting means is recorded on said movable storage medium and distance between said sensing means corresponding to the distance between said development electrode portions.

l0. The improvement as in claim 7 including a plurality of potential sources respectively associated with said development electrode portions, the potential sources being of successively smaller magnitude as the associated development electrode portions are more removed from the first development electrode portion to encounter the sheet. 

1. An electrophotographic device, characterized by gradually closing and gradually opening circuits for application of electric potential to the developing electrode so as to synchronize the application of electric potential with the relative movement of a sheet-shaped insulating material with respect to the developing electrode, whereby electric field will be generated only at the portion of the aforementioned developing electrode confronting the sheet-shaped insulating material while making a relative movement with reference thereto to cause the toner in the liquid developing agent to flow in the direction of the sheet-shaped insulating material.
 2. An electrophotographic device as claimed in claim 1, wherein the developing electrode is divided into smaller portions in the direction perpendicular to the direction in which the sheet is advanced.
 3. An electrophotographic device as claimed in claim 2, wherein said portions of the developing electrode are applied to the same potential.
 4. An electrophotographic device as claimed in claim 3, wherein later portions of the divided developing electrode are applied to decreased potential.
 5. An electrophotographic device which comprises a detector which detects the entry of a sheet-shaped material provided in the path of the sheet-shaped insulating material to a development station including a deveLoping electrode divided into smaller portions in the direction perpendicular to the direction in which the sheet is advanced, closing and opening circuits for application of electric potential to the portions of the developing electrode, and a delay circuit which receives the signal from said detector and makes said circuits close so as to apply electric potential only to the portions of the electrode confronting the sheet-shaped insulating material.
 6. An electrophotographic device as claimed in claim 5, wherein said delay circuit comprises a magnetic recording tape carried synchronously with the transportation of the sheet, a magnetic recording head confronting said recording tape and excited by the signal from the detector, and plurality of heads which read the signal on the tape and put out the signal to close and open said circuits for application of electric potential to the portion of the developing electrode.
 7. In an electrophotographic device comprising a container for a liquid developer having toner particles dispersed therein, and means including a carrier for moving a sheet of insulating material through said container, the improvement comprising a development electrode divided into a plurality of portions oriented perpendicular to the direction of movement of said sheet; detecting means for sensing the presence of said sheet along its path of movement; at least one source of potential; and actuating means responsive to said detecting means for sequentially energizing said development electrode means as said sheet is moved adjacent the successively energized development electrode portions and for sequentially de-energizing said development electrode portions as said sheet is moved away from the successively de-energized development electrode portions whereby said source of potential is only applied to those development electrode portions which are adjacent the sheet as it moves adjacent the development electrode so that the toner is substantially deposited only on the sheet and not the carrier therefor.
 8. The improvement as in claim 7 where said detecting means is disposed a predetermined distance from said development electrode, said improvement including delay means for delaying the output from said detecting means until the forward end of said sheet reaches the first of said plurality of development electrode portions.
 9. The improvement as in claim 8 where said delay means includes a movable storage medium, the output from said detecting means being recorded thereon, and where said actuating means includes (1) a plurality of switching means connected between said potential source and said plurality of development electrode portions respectively and (2) a plurality of sensing means successively disposed along a portion of said movable storage medium and respectively connected to said plurality of switching means, the first of said sensing means being disposed a predetermined distance from where the output from said detecting means is recorded on said movable storage medium and distance between said sensing means corresponding to the distance between said development electrode portions.
 10. The improvement as in claim 7 including a plurality of potential sources respectively associated with said development electrode portions, the potential sources being of successively smaller magnitude as the associated development electrode portions are more removed from the first development electrode portion to encounter the sheet. 